1. Field of the Invention
The present invention relates to a process for producing a light color high softening point hydrocarbon resin readily and advantageously on an industrial scale from a high boiling fraction obtained by the distillation of a cracked oil fraction which is obtained by thermal cracking of petroleum in the presence of a catalyst.
2. Discussion of Background
Heretofore, a process for producing a high softening point aromatic hydrocarbon resin by using a high boiling oil fraction obtained by the distillation of an oil fraction having a boiling point within a range of from 140.degree. to 280.degree. C. among cracked oil fractions obtained by thermal cracking of petroleum has been known and has already been employed on an industrial scale.
However, according to such a conventional process, it is usual that among cracked oil fractions obtained by thermal cracking of petroleum, an oil fraction having a boiling point within a range of from 140.degree. to 280.degree. C. is fed to a distillation tower, and a high boiling oil fraction withdrawn from the bottom of the tower is employed. Accordingly, the resin obtained by the polymerization of such a high boiling oil fraction as the starting material had various problems such that the color was poor, and the polymer yield was low. As a method for improving the color of this high softening point hydrocarbon resin, it is known to subject the above-mentioned high boiling oil fraction withdrawn from the bottom to further distillation and to use a fraction obtained from the tower top. It is also known to use a high boiling oil fraction obtained by side cutting, for example, by a chimney tray located below the feeding section of the distillation tower and above the bottom of the tower.
However, as a result of the study by the present inventors, it has been found that the above-mentioned side cutting method has drawbacks such that the distillation temperature is high, and when the residence time in the distillation tower is prolonged, the polymer yield tends to be low when the oil thereby obtained is used as a starting material for the production of a resin. Further, the above-mentioned method for repeating distillation is not necessarily economical although it has no particular problems with respect to the physical properties of the resin thereby obtained or with respect to the polymer yield.